Printers are devices that print images onto a printing medium such as a sheet of paper. Various types of printers exist offering a range of printing speeds, printing colors, and printing quality. Printers are commonly linked to computers (printing system) that generate the content of images, text, or graphics being printed.
Thermal inkjet printers (a type of ink jet printer) eject small drops of ink onto a printing medium, these droplets of ink form the image, text, and graphics generated by the computer. Modem inkjet printers are capable of producing photographic-quality images and are generally less expensive than conventional laser-type printers because the printing mechanism is less expensive to produce. Additionally, thermal inkjet printers are quiet (as compared to conventional impact printers) because there is no mechanical impact during the formation of the image other than the deposition of ink onto the printing medium. Thermal inkjet printers typically have a large number of individual ink-ejecting nozzles (orifices) disposed in a printhead. The nozzles are spatially positioned and are facing the printing medium. Beneath each nozzle is a heater resistor that thermally agitates the ink when an electrical pulse energizes the heater resistor. Ink residing above the heater resistor is ejected through the nozzle and towards the printing medium as a result of the electrical pulse. Concurrently, the printhead traverses the surface of the printing medium with the nozzles ejecting ink as instructed by the printing system. For high-speed printers, however, an array of printheads may be stationary relative to the printing medium while motion is imparted to the printing medium.
As ink is ejected from the printhead, the ink droplets strike the printing medium and then dry forming "dots" of ink that, when viewed together, create a printed image. Most thermal inkjet printing systems are constructed with a permanent printer body and a disposable or semi-disposable printhead. The printhead includes a die and a supporting substrate. Furthermore, ink may be supplied to the printhead from a reservoir attached to the printer. This configuration allows the printer to operate over an extended period of time prior to having the ink replenished.
In a conventional printhead, a die having disposed heater resistors and accompanying ink-ejecting nozzles is fluidically and electrically coupled to a substrate. The fluidic coupling of the die may be achieved by attaching the die to the substrate wherein ink flows to the heater resistors (disposed in the die) from the edge of the die or from the center of the die. In either configuration, however, the ink reaches the heater resistors and is available to be ejected onto the printing medium. Electrical connections (interconnects) are also made between the pen body and the die. In a conventional printhead, one of the pen body's functions (in view of the electrical coupling) is to support an interconnect circuit that supplies power to the die upon inserting the printhead into the printer.
The electrical coupling of a die to the substrate as performed in inkjet technology is sufficiently more complicated than electrically coupling a die to a substrate as commonly performed in conventional integrated circuit packaging. For example, the interconnects must be isolated from ink being ejected from the die due to the potential corrosiveness of ink. Additionally, certain constituents of the ink may be conductive thus causing electrical shorting of the interconnects. Secondly, the interconnects are exposed to continuous vibration and physical contact by the printer. The vibration is created, in part, from the traversing movement of the printhead relative to the printing medium whereas the physical contact between the printhead and the printer occurs during the cleaning cycle of the die. The cleaning cycle involves periodically passing a wiper across the die which removes ink residue and other particles that may degrade printing performance. Thirdly, the interconnects are exposed to a wide range of temperatures stemming from the printing demands of the computer system. Consequently, the temperature of the die may rise sharply followed by an immediate cooling period. Thermal cycling of the die as such may fatigue the electrical interconnects causing them to break.
Fluidic coupling of the die to the pen body may be equally challenging. Firstly, the vibration and cleaning of the printhead, as previously described, may create microcracks between the die and pen body interface. Consequently, ink may leak onto the printing medium, thus, ruining the image being printed. Additionally, the leaking ink may serve to degrade the electrical interconnects. In a similar manner, temperature variations may further exacerbate microcracking between the die and the pen body. A further consideration in view of fluidically (and electrically) coupling the die to the substrate is the distance between the printhead and the printing medium. In general, it is desirable to minimize this distance and thereby minimize errors in the trajectory of ink being ejected from the die.
Although many attempts have been made, and indeed are ongoing, to resolve challenges previously described in coupling the die to the pen body, there still remains a need for an improved printhead. An improved printhead as such would consist of electrical interconnects that are isolated from the ink and cleaning mechanism of the printer, electrical interconnects that are tolerant of rapid temperature changes and, an ink ejecting die that would operate in close proximity of the printing medium.